Okay, do politics matter? Absofuckinglutely. While I despise shoehorning the subject matter into everything, essentially all aspects of human society are political.
Which isn't to say that it has to be the determining factor in every choice everyone makes.
With this specific issue, mullvad and the donation made by one of the owners, it matters. You aren't required to care. You aren't required to agree. But it definitely matters when a company's profits are going straight to a political party. Doesn't matter if it's a party I agree with, it still matters, and I personally object to it when it's enough to change a political landscape.
But! That's me. If the use of money by capital to sway political outcomes doesn't bother you, that's fine you're essentially saying the same thing as a non voter: IDGAF, y'all sort this shit out.
Now, as far as specific party involved. I'm not certain neonazi is the right label. Definitely some questionable beliefs being at the forefront of their platform. But it isn't nazi either. I don't agree with their platform, and I think they're dangerous beyond the borders of their own country, but I can't point at them and say they're even fascist in the literal sense. They edge right up to it, but that's like saying an anarchist and a tankie are the same set of beliefs because they hate capitalism. There's more differences than similarities.
Which means I also can't point to someone staying with mullvad and say they're doing something bad either. I'm likely switching to ivpn when my mullvad time runs out, though of something better comes along, I'd consider it too.
But mullvad has a really good track record of backing up their claims of not having anything to give to any government. That's a pretty damn big deal to just dismiss. If that's someone's highest priority? I ain't mad at them. Nor would I entertain the screeching that goes along with someone saying that they don't care. There's a shit ton worse things in the world right now to worry about, and nobody has infinite energy for all of it.